1. Field of the Invention
The present invention relates to a deposition apparatus and a deposition method.
2. Description of the Related Art
Diamond deposition with use of a plasma CVD (Chemical Vapor Deposition) method has conventionally been performed. In such diamond deposition, a gas mixture of hydrogen and methane is used as a source gas to deposit a polycrystalline diamond film having a crystalline size of the order of micrometers (hereinafter referred to as an MD film).
In recent years, in the diamond deposition using the gas mixture of hydrogen and methane, a tendency for the crystalline size to rapidly decrease by setting a ratio of methane to 5% or more has been used to form a diamond film having a crystalline size of the order of nanometers (hereinafter referred to as an ND film). Such ND film having a crystalline size of the order of nanometers is smoother than the MD film, and therefore expected to be optically applied.
Also, in plasma CVD apparatus in semiconductor manufacturing, to improve uniformity of deposition, an electrode shape is changed to thereby control an active species density distribution and gas and electron temperatures in plasma, as disclosed in, for example, Unexamined Japanese Patent Application KOKAI Publication No. 2007-53359.
However, in the plasma CVD, if the electrode is formed in a complicated shape to achieve the uniformity of the deposition, electric field concentration is likely to occur in the vicinity of the electrode where electric field intensity is increased, and therefore some problems arise, for example, stable glow discharge required for the deposition is disturbed, and corona discharge or arc discharge is likely to occur.
Meanwhile, the present inventors have been advancing the development of a device material having excellent electron emission characteristics by depositing the nanodiamond film on an aggregate of a graphene sheet structure.
If, upon deposition of such ND film, the methane ratio in an atmosphere inside deposition apparatus is increased, a positive column (a region where a number of active species are included, and a substrate is typically placed so as to be exposed to the positive column) tends to shrink. For this reason, even in the case of the deposition with the same power, a local deposition rate is increased, but the uniformity of the deposition tends to be disturbed.
It is known that, upon deposition of the MD film, CH3 radicals known as a direct material for MD growth can diffuse in plasma because lifetimes of them in the plasma are relatively long, and are therefore uniformly distributed as compared with a density distribution, electron temperature distribution, and gas temperature distribution, of the other active species.
However, high chemical potential active species (C, C2, CH, or CxHy), which are to serve as material radicals for ND film growth, are rapidly decreased in density in a region where electron or gas temperatures is low. From this, it is considered that, in the ND film, an area where electron emission characteristics with respect to plasma expansion are uniform and the deposition is uniformly performed tends to be narrow as compared with the MD film.
Also, in an electron emission device using the ND film, electrical characteristics of a deposition surface are very sensitive to variations in substrate temperature and active species density in a deposition process, and therefore the electrical characteristics are likely to be influenced by variation in active species density distribution as described above. For this reason, in the deposition for the ND electron emission device, a deposition area where electrons can uniformly be emitted with respect to an applied voltage is smaller than an electrode area, and therefore in-plane uniformity becomes poor. Accordingly, there arises a problem that it is difficult to obtain the electron emission film capable of emitting electrons from the entire surface deposited on a substrate.
The present invention has been made in consideration of the above-described actual situations, and has an advantage of providing deposition apparatus and deposition method that are capable of forming a film having good uniformity in in-plane electrical characteristics.